Using the system's end of year or P46(car) File by Internet (FBI) functionality, the P11D Organiser will need to use your Government Gateway username and password in order to make the submission sucessfully.
During a test preparation or attempting to send a live submission, your username and password are authenticated with the Government Gateway, if they cannot be verified then the software will present a pop-up dialogue box to state the problem:-
Prepare Submission (Test submission)
Having run a test "preparation" should you decide to inadvertently use the "Send Submission" button to attempt to send the "live" submission before correcting the username and password problem...
Send Submission (live submission)
...the system's "Send Submission" button will then change to "View ERROR" button...
...which will display the XML file confirming the Gateway error.
Gateway XML file
Check your username and password with the Government Gateway:-
Once you have verified these with the Government Gateway, re-enter them in the P11D Organiser and you should now be able to make a successful submission.
Another cause can be the PAYE Reference name and number saved in the system have been entered incorrectly. Check these by viewing the COMPANY details screen and editing/changing these if they are incorrect.